1. Field of the Invention
The present invention relates to an array antenna device allowing the radiation direction of a beam to be changed and radio equipment using such device.
2. Description of the Related Art
An array antenna having a plurality of arranged radiator elements takes advantage of the easy synthesis of a directional pattern and is used in the field where high functions are required to be filled.
One characteristic feature of an array antenna is that high-speed beam scanning can be done. Up to now, the beam scanning in such array antennas is divided into two main classes of a mechanical scanning system and an electronic scanning system. In the electronic scanning system, there are (1) a phase scanning system, (2) a frequency scanning system, and (3) a scanning system including switching feed points.
In the phase scanning system ((1)), as shown in FIG. 16, the feed phase of each element antenna is controlled by a phase shifter, and the synthesis of a directional pattern is made.
In the frequency scanning system ((2)), the frequency characteristic of a feeder is utilized, and the synthesis of a directional pattern is made by changing the excitation phase of each element antenna.
In the scanning system of switching feed points ((3)), a beam is changed by selectively switching input points to a multi-terminal array antenna which is able to generate a multi-beam.
In the above frequency scanning system, the antenna itself is able to be relatively easily constructed, but as a wide frequency band is required the transmitter-receiver system becomes complicated. Further, in the phase scanning system, scanning with a high degree of freedom can be done in accordance with the control of phase shifters. However, because high-cost semiconductor elements and electronic switches for ultra high frequency applications are required in the phase shifters and their control circuit, there is a problem that low-cost systems cannot be realized as a whole. Further, in the scanning system of switching feed points, because the direction of a beam is changed by using hybrid circuits and phase shifters and switching input ports, the beam scanning becomes step-wise and accordingly the system is not suited for finer scanning and continuous scanning.
Moreover, in the mechanical scanning system, as shown in FIG. 17, scanning is conducted by rotating (swinging) the whole of a planar antenna using a motor and so on, and accordingly as the total antenna is displaced, there was a problem that the system becomes large-sized and heavy.